Acoustic blanket
An acoustic blanket absorbs acoustic energy and reduces noise in a launch vehicle. The acoustic blanket may be overlaid on a wall of a payload fairing of the launch vehicle. Materials and construction of the acoustic blanket allow for a relatively thin and light sound barrier. The acoustic blanket may comprise vertically-lapped polyester that is overlaid with a lightweight melamine foam. This combination of materials creates an acoustic impedance mismatch between layers that leads to absorption of acoustic energy across a relatively broad range of frequency bands. The acoustic blanket has a particular heat seal pattern that helps absorb noise while allowing the acoustic blanket to be relatively soft and flexible, which is useful for attaching the acoustic blanket to a curved wall of a fairing or other launch vehicle shapes. The acoustic blanket utilizes micro-perforations on multiple sides to allow for movement of air/venting while maintaining the bulk materials inside.
1 . An acoustic blanket comprising:
a melamine foam layer;
a first facing layer at least partially covering the melamine foam layer;
a polyester layer at least partially covering the melamine foam layer;
a second facing layer at least partially covering the polyester layer; and
air gaps between the polyester layer and the second facing layer, wherein the air gaps are partitioned from one another by a heat seal pattern between the polyester layer and the second facing layer, wherein a plan-view surface area ratio of the air gaps to the heat seal pattern is greater than 90% and the polyester layer is at least three times the density of the melamine foam layer.
2 . The acoustic blanket of claim 1 , wherein the second facing layer includes micro-perforations that allow for movement of air between the air gaps and outside the acoustic blanket.
3 . The acoustic blanket of claim 1 , wherein the polyester layer comprises a vertically-lapped polyester layer.
4 . The acoustic blanket of claim 3 , wherein the vertically-lapped polyester layer has a density of about 1.25 pounds per cubic foot.
5 . The acoustic blanket of claim 1 , wherein the first facing layer or the second facing layer is mylar.
6 . The acoustic blanket of claim 1 , wherein the melamine foam layer has a density of about 0.375 pounds per cubic foot.
7 . The acoustic blanket of claim 1 , wherein the first facing layer and the melamine foam layer comprise materials that can be heat sealed together.
8 . The acoustic blanket of claim 1 , wherein the second facing layer and the polyester layer comprise materials that can be heat sealed together.
9 . The acoustic blanket of claim 1 , wherein the heat seal pattern is substantially rectangular or square in plan view and comprises intersecting horizontal and vertical heat-sealed portions arranged in a staggered array to define the air gaps.
10 . The acoustic blanket of claim 2 , wherein the micro-perforations have micron-scale diameters and are arranged with millimeter-scale on-center spacing.
11 . A method of fabricating an acoustic blanket, the method comprising:
bonding, by heat sealing, a first facing layer and a melamine foam layer together so that the first facing layer at least partially covers the melamine foam layer in a first heat seal pattern;
bonding a polyester layer and the melamine foam layer together so that the polyester layer at least partially covers the melamine foam layer;
placing a second facing layer on the polyester layer so as to at least partially cover the polyester layer; and
heat sealing the second facing layer and the polyester layer together in a second heat seal pattern that forms air gaps between the polyester layer and the second facing layer, wherein a plan-view surface area ratio of the air gaps to the first or the second heat seal patterns is greater than 90%, and the polyester layer is at least three times the density of the melamine foam layer.
12 . The method of claim 11 , wherein the second facing layer includes micro-perforations that allow for movement of air between the air gaps and outside the acoustic blanket.
13 . The method of claim 11 , wherein the polyester comprises vertically-lapped polyester.
14 . The method of claim 13 , wherein the vertically-lapped polyester has a density of about 1.25 pounds per cubic foot.
15 . The method of claim 11 , wherein the first facing layer or the second facing layer is mylar.
16 . The method of claim 11 , wherein the melamine foam layer has a density of about 0.375 pounds per cubic foot.
17 . The method of claim 11 , wherein the side layers are permeable to allow for movement of air.
18 . The method of claim 11 , wherein the second facing layer includes a permeable membrane that allows for movement of air between the air gaps and outside the acoustic blanket.
19 . The method of claim 11 , wherein heat sealing the second facing layer and the polyester layer comprises applying a hot-melt seal material between the second facing layer and the polyester layer such that the seal material melts and bonds to each layer without melting either the second facing layer or the polyester layer.
20 . The method of claim 11 , further comprising heat sealing the first facing layer to the melamine foam layer in a third heat seal pattern that is substantially the same as the second heat seal pattern.